Let's check a few things first
Is the radio/stero aftermarket, if so it's probably turned on and draining the battery overnight. Many have wired them to stay on even with the car turned off. The gage problem, needs to be traced from the connector located on the back of the dash. If you have a Haynes manual for this vehicle, it will make it easier to trace where the wires are going to and whether they are finding a ground to drain the battery through an accessory left on. The alternator can also cause the problem if one of the diodes has gone bad allowing DC current to flow in both directions, thus draining the battery overnight. Try unplugging the alternator overnight and see if the battery goes dead. Remember to replug the alternator back in before starting the engine otherwise the current has no place to go and damage can be done to this critter.
Just some suggestions that are electrically common sense.